Using the knife tool on a plane (mesh) makes the cut incorrectly connect to the vertices irregularly
Alright, I honestly don't understand what you are asking. But a quick way to get any flat shape cutout is to delete all but one vertex. Then you can press E to extrude another vertex. These will be automatically connected. Make sure you are in vertex select mode by pressing 1 on the top row, or by pressing the vertex button. Then at the end, you can select your first and last vertex and press F to merge them. Then take all the vertices one side and press E to extrude them and they should extrude into faces. Now you can flatten all the vertices by pressing &quot;S&quot; for scale and pressing Zero. This will automatically shrink all your points into one, press either &quot;X, Y, OR Z&quot; until you get the one that you want. Pressing these will scale only on those axes.